CN107849939B

CN107849939B - Spoke mounting arrangement

Info

Publication number: CN107849939B
Application number: CN201680043510.4A
Authority: CN
Inventors: G.勒菲布维雷; R.斯恩诺特; J.皮伊特罗邦
Original assignee: Pratt and Whitney Canada Corp
Current assignee: Pratt and Whitney Canada Corp
Priority date: 2015-07-24
Filing date: 2016-07-12
Publication date: 2020-06-23
Anticipated expiration: 2036-07-12
Also published as: US20170107856A1; CA2935994A1; CN107849939A; US10443449B2; CA2935994C; WO2017015745A1

Abstract

A mid-turbine frame of a gas turbine engine has a structural ring assembly including an outer ring, an inner ring having a plurality of threaded projections extending from a radially outer surface thereof, and a corresponding number of structural spokes interconnecting the inner ring and the outer ring. Each spoke has a radially inner threaded end that is threadedly engaged in an associated one of the threaded protrusions on the inner ring.

Description

Spoke mounting arrangement

Related patent application

This application claims priority from U.S. patent provisional applications nos. 62/196,360 and 62/196,330 filed on 24/7/2015, the entire contents of which are incorporated herein by reference.

Technical Field

The present application relates generally to gas turbine engines and, more particularly, to spoke mounting arrangements.

Background

It is known to use structural spokes to transfer loads from the bearing housing to the outer structural ring of the gas turbine engine. Such spokes may be found, for example, in mid-turbine frame modules. Each spoke extends generally radially from the outer ring through a strut in the gas path to the inner ring supporting the bearing housing. Typically, a mounting pad and a plurality of bolts with shim spacers are used to attach the inner end of each spoke to the inner ring and adjust the position of the inner ring relative to the outer ring. The use of machined gaskets/spacers increases the final stack-up, increases the number of engine components and increases the complexity of the overall assembly.

Disclosure of Invention

In one aspect, a simple way of attaching the inner ends of the spokes to the inner structural ring using threads on the radially inner ends of the spokes for threaded engagement with corresponding threaded protrusions integral with the inner structural ring is provided.

According to another aspect, an inner structural ring adapted to receive and support a bearing housing is provided, the inner structural ring having circumferentially spaced apart threaded projections on a radially outer surface thereof for threaded engagement with mating threads at a radially inner end of a respective spoke.

According to another aspect, a structural ring assembly is provided that includes an outer ring, an inner ring having a plurality of threaded projections extending from a radially outer surface thereof, a corresponding number of structural spokes interconnecting the inner and outer rings, each spoke having a radially inner threaded end threadably engaged in an associated one of the threaded projections on the inner ring.

According to another aspect, a turbine mid-frame for a gas turbine engine is provided, comprising: an outer ring, an inner ring, and a plurality of circumferentially spaced apart spokes structurally interconnecting the inner ring and the outer ring, the spokes having a radially inner threaded end threadably engaged to the inner ring and a radially outer end positioned to apply a force in a radially outward direction against a radially inner surface of the outer ring, thereby maintaining the spokes in compression between the inner ring and the outer ring.

According to another aspect, a gas turbine engine is provided that includes a first turbine section, a second turbine section, and a turbine mid-frame axially located between the first and second turbine sections, the turbine mid-frame comprising: an outer structural ring, an inner structural ring configured to support a bearing, a plurality of load carrying spokes structurally interconnecting the outer structural ring and the inner structural ring, each load carrying spoke having a radially inner threaded end threadably engaged with mating threads integrally formed in the inner structural ring and a radially outer end mounted in bearing contact against a radially inner surface of the outer structural ring, thereby maintaining the load carrying spokes in compression between the inner and outer structural rings.

According to yet another general aspect, there is provided a method of axially assembling a turbine mid-frame for use in a gas turbine engine between a first turbine section and a second turbine section, the method comprising: threadably engaging a respective radially inner threaded end of each spoke with a corresponding threaded region disposed at circumferentially spaced apart locations around the periphery of the inner structural ring; centering the inner structural ring relative to the outer structural ring, wherein centering comprises adjusting a length of the spokes that project radially outward from the inner structural ring by: rotating the spokes about their respective longitudinal axes until their respective radially outer ends abut and exert a radially outward force on the radially inner surface of the outer structural ring; and then fastening the radially outer ends of the spokes to the outer structural ring to secure the spokes in a compressed state between the inner and outer structural rings.

Drawings

Referring now to the drawings wherein:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is an isometric view of a turbine mid-frame module;

FIG. 3 is another isometric view of the mid-turbine frame module, but with the integral strut-blade shells omitted to better illustrate the structural spokes extending between the inner and outer structural rings;

FIG. 4 is an enlarged isometric view showing the inner ends of the spokes threadably engaged in threaded protrusions extending from the radially outer surface of the inner structural ring;

FIG. 5 is a cross-sectional view showing the radially inner end of the spoke threadably engaged in a threaded projection on the inner structural ring.

FIG. 6 is an exploded isometric view showing the bolted connection between one of the spokes and the outer structural ring; and

figure 7 is an isometric view illustrating the anti-rotation feature of the bolted connection shown in figure 6.

Detailed Description

FIG. 1 illustrates a turbofan gas turbine engine 10, preferably of the type configured for use in subsonic aircraft, generally including a fan 12 in serial flow communication with ambient air being propelled by the fan 12; a multistage compressor 14 for pressurizing air; a combustor 16 in which the compressed air is mixed with fuel and ignited to generate an annular flow of hot combustion gases; and a turbine section 18 for extracting energy from the combustion gases.

FIG. 2 illustrates a portion of turbine section 18. More specifically, FIG. 2 illustrates a mid-turbine frame module 20 adapted to be axially mounted between a first turbine section and a second turbine section. The mid-turbine frame module 20 includes an inner structural ring 22 adapted to receive and support a bearing housing 23 (see FIG. 5), which bearing housing 23 is correspondingly adapted to support the main shaft of the engine 10. As shown in fig. 5, the bearing housing 23 may be detachably mounted to the inner ring by means of bolts 25. Referring now to fig. 2 and 3 concurrently, it can be seen that the inner structural ring 22 is structurally supported by the outer structural ring 24 by means of a plurality of circumferentially distributed spokes 26 (6 in the illustrated embodiment). In addition to transferring loads from the inner ring 22 to the outer ring 24, the spokes 26 are also used to center the inner ring 22, and thus the bearing housing 23, relative to the outer ring 24.

Each spoke 26 may extend radially through a hollow strut 27 (fig. 5) of a non-structural integral strut-vane housing 28 (fig. 2) that is "floatingly" mounted between the inner and outer

structural rings

22, 24 to direct combustion gases between two axially adjacent turbine stages. The casing 28 has a radially outer gas path wall 28a and a radially inner gas path wall 28b (FIG. 5) defining a portion of the gas path of the turbine section 18 therebetween. According to the illustrated embodiment, the housing 28 is not structural. I.e. the load from the bearing housing 23 is not transferred to the outer housing 24 via the integrated strut-blade housing 28. Rather, the load is transmitted through the spokes 26, the spokes 26 being shielded from the hot combustion gases by the hollow struts 27 of the integrated strut-blade shell 28. In such an arrangement, the spokes can be referred to as cold spokes.

As best shown in fig. 3-5, each spoke 26 is threadably engaged at its radially inner end with a threaded projection 30 integrally formed on the inner ring 22. According to the illustrated example, the external thread at the radially inner end of the spoke engages with a matching thread of an internally threaded projection 30, which internally threaded projection 30 projects radially outwards from the radially outer surface of the inner ring 22. It should be noted that the threaded protrusion 30 can extend from the radially inner circumferential surface of the inner ring 22 and is therefore not limited to being disposed on the radially outer surface of the inner ring. The protrusions can be provided at various radial/circumferential locations on the inner ring. Also, it should be understood that internal threads can be provided on the spokes and external threads can be provided on the protrusions. Moreover, each threaded portion on the inner ring 22 can also take on a variety of suitable configurations to provide the desired thread length.

The threads on the spokes 26 may be machined simultaneously with the turning operation of the spokes. The inner ring 22 may be cast, machined or otherwise suitably fabricated in the form of a simple ring having circumferentially spaced apart threaded protrusions on one of its radially outer or inner surfaces.

The above arrangement provides a simple and effective way of adjustably attaching the spokes 26 to the inner ring 22 supporting the bearing housing 23. No additional fasteners or attachment parts are required. It provides a compact design allowing for an improved aerodynamic gas path (there is additional radial space available for modification of the inner gas path wall 28a and the outer gas path wall 28 b). The threaded connection between the inner ends of the spokes and the inner ring 22 reduces the accumulation of misalignment and simplifies the bearing housing centering process compared to conventional spoke mounting arrangements with gaskets, bolts and gasket spacers.

As best shown in fig. 6 and 7, each spoke 26 may be bolted at its radially outer end to the outer structural ring 24. At each assembly point, a seat 31 for receiving a washer 32 is defined in the radially outer surface of the outer ring 24. The washer 32 may have a flat body with circumferentially spaced apart holes 34 defined therein for individually receiving respective bolts 36 or equivalent threaded fasteners (4 in the illustrated example). A corresponding elongated mounting slot 38 is defined in the bottom of the seat 31 for receiving the bolt 36. Each slot 38 is permitted to align with at least one corresponding threaded hole 40 in an annular array of holes defined in a mounting flange or head 42 at the radially outer end of the spoke 26. Thus, the washer 32 is positioned in its associated seat 31 such that the apertures 34 defined therein are aligned with the corresponding apertures 40 of the mounting flange of the spoke 26. After the holes 34 in the washer 32 have been properly angularly aligned with the corresponding holes 40 in the mounting flange of the spokes 26, the bolts 36 are tightened to securely join the spokes 26 to the radially inner circumferential surface of the outer structural ring 24.

As shown in fig. 6 and 7, the washer 32 may be provided with a pair of anti-rotation tabs 42 at each aperture 34. In accordance with the illustrated embodiment, each pair of anti-rotation tabs 42 includes a first tab 42a on the inner diameter of the washer 32 and an oppositely facing second tab 42b on the outer diameter of the washer 32. As shown in fig. 7, each pair of first and

second tabs

42a, 42b may be bent out of the plane of the washer 32 into engagement with the head of the associated bolt 36 to positively lock the head against rotation. In the illustrated embodiment, each pair of anti-rotation tabs 42 may engage opposite sides of the hex head of the associated bolt 36. This effectively prevents loosening of the bolt 36. While deformable or bendable tabs have been shown, it should be understood that any suitable type of locking tab could be used.

Referring to fig. 6, it can be seen that the peripheral portion of the washer may be deformed into an anti-rotation notch or catch 46 disposed at a location around the periphery of the washer seat 30. According to one embodiment, after all of the bolts 36 have been tightened and locked in place with the tabs 42, a peripheral portion of the washer 32 can be stamped into the anti-rotation catch 46. This prevents rotational movement of the washer 32 relative to the outer housing 24, thereby locking the spokes 26 against rotation about their longitudinal axes.

During assembly of the mid-turbine frame, the threaded engagement of the spokes 26 in the threaded projections 30 is adjusted by rotating the spokes 26 about their respective axes in either a clockwise or counterclockwise direction depending on the direction of the threads so that the radially outer ends of the spokes 26 firmly abut the radially inner circumferential surface of the outer ring 24. Each spoke is rotated so as to adjust the length of the portion of the spoke that projects radially outward from the inner ring 22. The spokes are unthreaded until the radially outer ends of all the spokes uniformly abut the inner surface of the outer ring. The spokes are adjusted in length such that each spoke exerts a force directed in a radially outward direction against the inner surface of the outer ring. These forces should be consistent throughout the entire ring. Once all of the spokes have been appropriately adjusted to collectively center the inner ring relative to the outer ring, the bolts 36 can be threadedly engaged from outside the outer ring with corresponding threaded holes defined in the heads of the spokes at the radially outer ends of the spokes.

Those skilled in the art will recognize that the spokes 26 are mounted in compression between the radially inner ring 22 and the outer ring 24. That is, as described above, the load carrying spokes 36 are pre-stressed into compression during engine assembly. Thus, compression is always maintained on the threads at the radially inner and outer ends of the spokes 26. This helps to prevent loosening of the threaded connections at both ends of the spokes. During engine operation, when the spokes 26 are exposed to heat, the spokes tend to expand, thereby further increasing the pressure on the threads and thus preventing loosening. The advantages of constructing spokes prestressed into compression are 2: 1) the amount of assembly pre-stress is minimized, facilitating assembly, and as the spokes thermally expand during engine operation, they will act against the inner and outer rings, thereby increasing the compressive load in the spokes. If the spokes are assembled in tension, the level of pre-stressed tension will be thermally reduced during engine operation, and the threaded connection is therefore subject to loosening. This can lead to problems with bearing decentration. As can be appreciated from the foregoing, these problems can be overcome by assembling the spokes in a compressed state. Engine operation will only increase the amount of compression thereby further preventing loosening of the threaded connection.

The above description is intended to be exemplary only, and those skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Any modifications that fall within the scope of the invention will be readily apparent to those skilled in the art from a review of this disclosure, and such modifications are intended to fall within the appended claims.

Claims

1. A mid-turbine frame of a gas turbine engine, comprising: an outer ring, an inner ring, and a plurality of circumferentially spaced apart spokes structurally interconnecting the inner ring and the outer ring, the spokes having radially inner threaded ends threadably engaged to the inner ring and radially outer ends positioned to apply a force in a radially outward direction against a radially inner surface of the outer ring, thereby maintaining the spokes in compression between the inner ring and the outer ring.

2. The mid-turbine frame defined in claim 1, wherein threaded fasteners extend through the outer ring in threaded engagement with radially outer ends of the spokes.

3. The mid-turbine frame defined in claim 2, wherein the threaded fasteners include bolts threadably engaged with threaded holes defined in the radially outer ends of the spokes.

4. The mid-turbine frame defined in claim 1, wherein each of the spokes has a flange at a radially outer end thereof in bearing contact with a radially inner surface of the outer ring, at least two holes being defined in the flange, the holes being aligned with slots defined through the outer ring for receiving fasteners.

5. The mid-turbine frame defined in claim 1, wherein circumferentially spaced apart projections are integrally formed on the inner ring, and wherein threads are formed in the projections for engagement with the spokes.

6. The mid-turbine frame defined in claim 5, wherein the protrusion extends radially outward from a radially outer surface of the inner ring.

7. The mid-turbine frame defined in claim 1, wherein the spokes are threadably engaged with threads integrally formed on the inner ring.

8. A gas turbine engine comprising a first turbine section, a second turbine section, and a turbine mid-frame axially located between the first and second turbine sections, the turbine mid-frame comprising: an outer structural ring, an inner structural ring configured to support a bearing, a plurality of load carrying spokes structurally interconnecting the outer structural ring and the inner structural ring, each load carrying spoke having a radially inner threaded end threadably engageable with mating threads integrally formed in the inner structural ring and a radially outer end mounted in bearing contact against a radially inner surface of the outer structural ring, thereby maintaining the load carrying spokes in compression between the inner and outer structural rings.

9. The gas turbine engine of claim 8, wherein each of the load carrying spokes exerts a force in a radially outward direction against a radially inner surface of the outer structural ring.

10. The gas turbine engine of claim 8, wherein threaded fasteners extend through the outer structural ring into threaded engagement with radially outer ends of the load carrying spokes.

11. The gas turbine engine of claim 10, wherein the threaded fasteners comprise bolts threadably engaged in threaded bores defined in radially outer ends of the load carrying spokes.

12. The gas turbine engine of claim 8, wherein each of the load carrying spokes has a flange at a radially outer end thereof in bearing contact with a radially inner surface of the outer structural ring, at least two holes being defined in the flange, the holes being aligned with corresponding slots defined through the outer structural ring for receiving fasteners.

13. The gas turbine engine of claim 8, wherein circumferentially spaced apart projections are integrally formed on the inner structural ring, and wherein the mating threads are formed in the projections.

14. The gas turbine engine of claim 13, wherein the protrusion extends radially outward from a radially outer surface of the inner structural ring.

15. The gas turbine engine of claim 8, wherein the mating threads are integral with the inner structural ring.

16. A method of axially assembling a turbine mid-frame for use in a gas turbine engine between a first turbine section and a second turbine section, the method comprising: threadably engaging a respective radially inner threaded end of each spoke with a corresponding threaded region disposed at circumferentially spaced apart locations around the periphery of the inner structural ring; centering the inner structural ring relative to the outer structural ring, wherein centering comprises adjusting a length of the spokes that project radially outward from the inner structural ring by: rotating the spokes about their respective longitudinal axes until their respective radially outer ends abut and exert a radially outward force on the radially inner surface of the outer structural ring; and then securing the radially outer ends of the spokes to the outer structural ring to secure the spokes in compression between the inner and outer structural rings.

17. The method of claim 16, wherein fastening includes bolting each spoke to the outer structural ring.

18. The method of claim 16, wherein adjusting the length comprises partially untwisting the spokes from the inner structural ring.

19. The method of claim 16, wherein threadably engaging comprises threadably engaging the spokes with threaded protrusions integrally formed on the inner structural ring at each of the threaded locations.